rcu: Fix FIXME in rcu_tasks_kthread()

This commit affines rcu_tasks_kthread() to the housekeeping CPUs
in CONFIG_NO_HZ_FULL builds.  This is just a default, so systems
administrators are free to put this kthread somewhere else if they wish.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 3ef8ba5..8a39e68 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -531,7 +531,8 @@
 	struct rcu_head *next;
 	LIST_HEAD(rcu_tasks_holdouts);
 
-	/* FIXME: Add housekeeping affinity. */
+	/* Run on housekeeping CPUs by default.  Sysadm can move if desired. */
+	housekeeping_affine(current);
 
 	/*
 	 * Each pass through the following loop makes one check for